Simulation Study On Freeze-out Temperature And Radial Flow In Sub-GeV Energies

The heavy-ion collisions at sub-GeV energies are of special significance for the study of the properties of nuclear matter at low temperature and high density, despite that the form of the nuclear equation of state in this energy region is still not revealed. The radial flow, the predominant collection flow phenomenon in central collisions, is considered useful in the study of the nuclear matters in extreme conditions. The HIRFL-CSR in Lanzhou is the only nuclear experiment facility working at sub-GeV energies in China,which will bring unique opportunities to the study of high-energy nuclear physics. This dissertation is intended as a model prediction for the upcoming External-target Experiment at HIRFL-CSR.In this Dissertation, we use the IQMD model to simulate central Au + Au collisions at sub-GeV energies, calculate the thermalization parameter and radial flow and obtain the temperature of the particle source by fitting the nucleon inclusive transverse-mass spectra with the widely-used Blast-wave model. By grouping particles by their freeze-out time, we analyze the time evolution properties of these quantities. Based on these, the dependencies upon mean field, nucleon-nucleon cross sections, incident beam energies and isospin effects of these quantities are also discussed. We find that the thermalization has a strong dependency on the mean field, while being insensitive to the nucleon-nucleon cross sections. Higher beam energy leads to faster thermalization. A large radial flow can be generated without mean field, while its dependencies upon the mean field and nucleonnucleon cross sections are rather weak. Higher beam energy generates larger flow with a similar flow pattern. The softer EoS corresponds to higher temperature in flow element,which is also insensitive to the nucleon-nucleon cross sections. The similar pattern of time evolution of temperatures indicate that the thermal motion is independent of beam energy,and the differences of beam energies are only manifested in collective flow. By comparing thermalization parameters, radial flows and temperatures of both proton and neutron, we find that these quantities are all insensitive to the isospin degrees of freedom contained in the mean field and nucleon-nucleon cross sections.